1. Field of the Invention
The present invention relates generally to a nonlinear optical device. More particularly, the present invention relates to a wavelength conversion device package with less optical loss for stabilizing optical alignment under an external environmental change, for example, in a temperature variation by providing a temperature regulating block and a temperature sensor to an optical oscillator and a wavelength modulator and fixing a flexible optical transmitter to the optical oscillator and the wavelength modulator.
2. Description of the Related Art
A laser light source technology using a polarization-inverted nonlinear chip is applied in various manners. For example, Difference Frequency Mixing, Sum Frequency Mixing, or Optical Parametric Oscillator can be achieved.
To produce the wavelength light source in the visible light band, a second harmonic generation which is a special form of the frequency, is adopted. The second harmonic generation projects a pumping light source having the low frequency into a polarization-inverted nonlinear optical waveguide and converts to a light source having the double frequency. In theory, the power of the second harmonic light source is determined in proportion to the square of the incident pumping light source power and the square of the length of the nonlinear chip. However, the conversion efficiency of 100% is not attained because of a loss in the optical waveguide, an absorption loss, an optical interconnection loss, and so on. A representative example of the second harmonic generation using the nonlinearity is a wavelength conversion laser device.
In the manufacture of the wavelength conversion laser using the nonlinearity, important variables include a nonlinear coefficient value of a crystal, a length of a nonlinear sample, a power of the input pumping light source, a line width of the input pumping light source, an alignment loss and a temperature stabilization of the pumping light source and the optical waveguide, a mode of the optical waveguide, and a waveguide loss of the optical waveguide. To package the waveguide including the polarization-inverted area, it is necessary to apply two temperature stabilization modules to the laser diode and the polarization-inverted waveguide respectively. In so doing, the misalignment is caused according to respective temperature stabilization set values and thus the optical connection power varies. The location change of about 1 micron gives rise to the optical connection power variation of 10%. In result, disadvantageously, the power of the wavelength-converted light source is subject to the loss. A power conversion efficiency to the wavelength conversion light source is proportional to the power of the input pumping light source. Correspondingly, the power loss of 10% leads to the conversion efficiency reduction of 10%.
FIG. 1 is a diagram of a conventional nonlinear optical oscillator using a laser diode.
The conventional nonlinear optical oscillator includes a laser diode 120 for outputting the laser, an optical condenser lens 150 for condensing the output laser and projecting the condensed laser to a Ti diffused waveguide 160 of which polarization 130 is periodically inverted on a ferroelectric crystal 140, and an optical collimating lens 170 for calibrating the focus of the laser light output from the optical waveguide 160.
The conventional Ti diffused waveguide features the waveguide mode control and the minimum waveguide loss, whereas it suffers a material problem in a photorefractive effect. The photorefractive effect indicates the change of the refractive index according to the intensity of the light source passing through the optical waveguide. In general, the Ti diffused waveguide is subject to the photorefractive effect even in the input light source of 1 mW. Hence, the wavelength conversion laser based on the Ti diffused waveguide can produce only the light source less than 1 mW. Mostly, when the optical connection using the lenses 150 and 170 is adopted, the alignment is complicated and the interconnection loss is quite considerable.
After the optical condenser lens, the Ti diffused waveguide, and the optical collimating lens are aligned in the path of the laser light output from the laser diode, the optical power sensitively varies according to the external environment change and the set temperature.
FIG. 2 is a diagram of another conventional nonlinear waveguide.
An optical waveguide 210 generates periodic polarization inversion a and b by depositing TiO2-doped-Ta2O5 over a LiNbO3 nonlinear crystal wafer 220, forming a thin film, and then patterning.
The cycle of the periodic polarization inversion grating is determined by the wavelength of the second harmonic to generate. By controlling the thickness and the width of the TiO2-doped-Ta2O5 thin film and the refractive index variation (2.2˜2.4) based on the doping amount, the guided mode of the pumping light source and the second harmonic is optimized.
When the optical waveguide including the polarization-inverted area in a rib structure is formed using the thin-film deposition, the photorefractive effect of the diffused waveguide can be mitigated to some degree. However, since the ratio of Ti/(Ti+Ta) is regulated to control the refractive index, the photorefractive effect can be caused.
In addition, the optical connection method using the conventional lens causes the optical connection loss according to the temperature regulation.
Particularly, the conventional optical waveguides are subject to the difficult alignment of the laser optical path because of the external environment factors. As a result, it is hard to realize its product implementation in lack of specific methods for optimizing the loss of the input light source and the optical waveguide and enhancing the structure for the selection and the compactness of the packaging structure when the device is fabricated.